Pen



FIG. 1 is a front view of a pen showing my new design;

FIG. 2 is a side view thereof which is a mirror image of the opposite side thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a top view thereof; and,

FIG. 5 is a bottom view thereof. 

The ornamental design for a pen, as shown and described. 